This invention relates to a pressure transucer suitable to be used as a pressure detector for automobiles.
Pressure transucers are widely used for automobiles. For example, the following usages are known, that is, they are a method for keeping a most suitable combustion condition of an engine by controlling an amount of fuel injected by an electron fuel injector and the advance angle of an electron angle-advancing device, with electric signals obtained by detecting and converting the pressure difference between the pressure in the suction pipe of the engine and the atmospheric pressure or the absolute pressure, a method for compensating the altitude by detecting the atmospheric pressure changing according to the altitude, a method for indicating the pressure to the driver of an engine by detecting the pressure in the suction pipe of the engine, etc.
Hitherto, as means for indicating the suction pipe pressure of the engine of a car to the driver operating the car, a Bourdon-tube pressure gauge is used. In this case, the gauge is disposed in the car room, and the pressure in the suction pipe is introduced from the engine room into the gauge through a pressure induction pipe. In such an arrangement of the pressure gauge, if the pressure induction pipe is disengaged from the pressure gauge, a non-combustion gas, a combustion gas for EGR (exhaust gas recirculation) enter the car room to leave persons in the car room under the dangerous condition. Therefore, there is proposed a method in which only an indication board is disposed in the car boom, and a pressure detector disposed in the engine room transmits electric signals to the indication board whereby the pressure in the suction pipe is displayed on the indication board.
In the case where a pressure detector such as a pressure transducer is disposed in the engine room, particularly in case where an amplifier is incorporated in the interior of a pressure detector for amplifying electric signals obtained by converting the pressure difference detected thereby, it is necessary for the pressure detector to be waterproof, because changes in the characteristics of the pressure detector, diminished conductivity, etc. due to the rust may occur. On the other hand, if the pressure detector is made completely airtight as shown in FIGS. 2, 6, 7 of U.S. Pat. No. 3,568,124, reference pressure in the airtightly closed chamber changes according to the change of volume of the air in the closed chamber caused by the change of temperature in the surroundings of the pressure detector, therefore precision of performance of the pressure detector is greatly reduced.